The present study was carried out in order to investigate the nature of the increase in the cerebrospinal fluid (CSF) protein content described in diabetic neuropathy. The CSF proteins were studied in 22 patients with clinical signs of diabetic neuropathy. The total protein content and the electrophoretic pattern (paper electrophoresis) of the proteins were studied in one CSF sample of each patient. The CSF sample was collected through lumbar puncture. For comparative purposes, the total protein content and the electrophoretic pattern of the blood serum proteins were determined in 17 patients. For the same purpose the impairment of the nervous system was evaluated in a semi-quantitative way. The CSF protein concentration was increased in 7 cases (32%). The increases were slight. The electrophoretic patterns were found to be similar to those found in normal conditions. The relative values found for each of the protein fractions were increased in some instances. Such increases were slight and did not change the protein pattern of the CSF. Among these changes, that regarding the y-globulin was observed in 3 cases. The CSF protein pattern did not show changes related to the total protein content of the sample. Changes in the serum protein pattern did not induce changes in the CSF protein pattern. The correlation between the total protein content of CSF and serum was not statistically significant. In the cases studied no statistically significant correlation between the degree of neurological involvement and the CSF proteins was found. However, the data suggest a trend to correlation between the neurological picture and the total protein content of the CSF, particularly with β-globulin.The results show that the increase in the total protein content of the CSF in diabetic neuropathy is not related to changes regarding one or more of the protein fractions of CSF. It is not dependent also on the protein concentration in the blood serum and/or the changes found in its protein pattern. The degree of the nervous impairment in itself cannot be directly related to the increase in the CSF proteins. The importance of damage in the blood-CSF barrier is pointed out by data of the literature concerning the protein fractions in diabetic patients. Such damage cannot be excluded in the discussion of the results found. Its presence would enhance the passage of proteins to the CSF, thus resulting an increase in the total protein content. Changes in the protein pattern in such conditions are absent or slight, as it was found in the cases studied.